This invention relates to air conditioning and ventilation systems in general, and specifically to a drive for a flexible film belt damper with a position indicator that can be easily aligned to the belt.
A relatively recent trend in automotive air conditioning and ventilation systems has been the replacement of conventional, swinging flapper door valves with flexible film belts. A run of flexible film is rolled back and forth between a take up roller and a drive roller, and a window in the belt covers and uncovers an air passage within a housing of the system, allowing air through in direct proportion to the degree that the opening is uncovered. This promises more predictable control of airflow rates, as well as a potentially more compact system.
One advantage of the conventional, swinging flapper door is that it swings over less than a full turn, and it is therefore relatively easy to monitor its position. One known device is a potentiometer, in which a wiper that turns with the flapper door shaft wipes along an annular ring, back and forth, creating a changing resistance. The potentiometer works only over less that a full 360 degrees, but that comports with the operation of a swinging flapper door. The rollers that run the film belt must move through multiple turns, however. Therefore, if a potentiometer is to be used as a position indicator, a series of reduction gears must be used to step down the multiple turns of the belt roller into a single turn of the potentiometer. While that can be easily done, the potential exists for misaligning the potentiometer relative to the drive mechanism when the various gears are removed and replaced, such as during servicing. This misaligning will not be easily visible to the operator, but will throw off the position indicating function of the potentiometer.
The subject invention provides a means for re aligning the potentiometer if it becomes misaligned, which is simple and compact and works in conjunction with the basic, normal operation of the film belt.
In the preferred embodiment disclosed, the belt runs between normal left and right limit positions. Reduction gears operable between one of the belt rollers and the potentiometer translate the multiple turns of the belt roller into just less than a full turn of the potentiometer wiper. Therefore, the limit positions of the belt correspond to limit positions of the potentiometer wiper on the ring.
The potentiometer wiper is not directly turned by the reduction gear mechanism, however. Instead, a slip clutch is superimposed, so as to indirectly drive the potentiometer wiper. A tab extends radially from the potentiometer wiper, and engages one of two hard stops on the HVAC case when the potentiometer wiper is in either of its limit positions. If the potentiometer and the gear mechanism are properly aligned, the engagement of the hard stops will correspond to the belt also being at its limit positions. However, if the potentiometer and gear mechanism are misaligned, in either direction, the tab on the potentiometer wiper will hit one of the hard stops before the belt has reached its limit position. The belt will continue to roll past that point, but the slip clutch will shift as the tab is pushed against the hard stop, thereby allowing potentiometer wiper to stay at its limit position until the belt reaches its limit position. At that point, the limit positions of the potentiometer and belt will again properly correspond.